Molluscs from a shallow-water whale-fall and their affinities with adjacent benthic communities on the Swedish west coast

Abstract

We conducted a species-level study of molluscs associated with a 5-m long carcass of a minke whale at a depth of 125 m in the Kosterfjord (North Sea, Sweden). The whale-fall community was quantitatively compared with the community commonly living in the surrounding soft-bottom sediments. Five years after the deployment of the dead whale at the sea floor, the sediments around the carcass were dominated by the bivalve Thyasira sarsi, which is known to contain endosymbiotic sulphur-oxidizing bacteria, while background sediments were dominated by another thyasirid, T. equalis, less dependent on chemosynthesis for its nutrition. The Kosterfjord samples were further compared at the species level with mollusc abundance data derived from the literature, including samples from different marine settings of the west coast of Sweden (active methane seep, fjords, coastal and open marine environments). The results show high similarity between the Kosterfjord whale-fall community and the community that developed in one of the Swedish fjords (Gullmar Fjord) during hypoxic conditions. This study indicates that at shallow-water whale-falls, the sulphophilic stage of the ecological succession is characterized by generalist chemosynthetic bivalves commonly living in organic-rich, sulphidic environments.

Key words:

• Whale
• Thyasiridae
• organic-enriched sediments
• chemosynthesis
• North Atlantic

Acknowledgements

The authors thank Tomas Lundälv of the RV Lophelia for assistance with ROV operations and video documentation; Ingemar Adolfsson, Anders Billing of the RV Nereus for assistance with sampling; Helena Wiklund for help with sample processing and Anders Warén for help in species identification. A special thanks to Alf Josefson for providing copies of the Gullmar Fjord reports. Adam Tomašových and Martin Zuschin are thanked for assistance in interpreting the possible influence of taphonomic effects on the results. We thank also two anonymous reviewers for their useful comments which helped in improving the manuscript. We dedicate this manuscript to the late Hans G. Hansson for inspiring discussions and the early suggestion to sink a whale in the Koster area. Funding was provided to TGD by the Swedish Research Council.

Editorial responsibility: Christiane Todt